The fetal antigen hypothesis: cancers and beyond.

Twenty years ago the fetal antigen hypothesis was proposed as a potential mechanism by which women are naturally immunized against cancer antigens by antigens from their fetus. Evidence from recent clinical studies shows that a high percentage of parous woman, but not nulliparous women, show evidence of immunization to antigens found on breast, ovarian and endometrial cancer cells. I suggest that this maternal immunization also affects the fetus, causing early immune rejection of fertilized ova that express cancer-related genotypes. Additional cancers, and perhaps even other types of genetic diseases, may be involved in this mechanism.